Method and device for carrier envelope phase stabilisation

ABSTRACT

A method of stabilizing a carrier envelope phase of laser pulses generated with a laser device, comprising the steps of generating laser pulses with a seed laser unit, amplifying the laser pulses with an amplifier unit, generating an amplifier output signal derived from the laser pulses amplified with the amplifier unit, and controlling the carrier envelope phase of the laser pulses with an amplifier loop based on the amplifier output signal, wherein the controlling step comprises a step of adjusting an optical path of the amplifier unit in dependence on the amplifier output signal, wherein the adjusting step comprises introducing a dispersive material into the optical path of the amplifier unit. Furthermore, a stabilizing device for stabilizing a carrier envelope phase of laser pulses and a laser device including at least one stabilizing device are described.

RELATED APPLICATION

This is a §371 of International Application No. PCT/EP2006/011561, withan international filing date of Dec. 1, 2006 (WO 2008/064710 A1,published Jun. 5, 2008).

TECHNICAL FIELD

The present disclosure relates to a method of stabilising a carrierenvelope phase (CE-phase) of laser pulses, in particular for carrierenvelope phase stabilisation in femtosecond laser amplifier systems.Furthermore, the present disclosure relates to devices of stabilising aCE-phase of laser pulses, in particular for implementing the stabilisingmethod.

BACKGROUND

Recent advances in the research on the interaction of ultrashort laserpulses with matter have shown that the outcome of many processes dependson the relative phase between the pulse envelope and the carrier wave,also called carrier envelope phase (CE-phase), see G. G. Paulus et al.in “Nature”, vol. 414, 2001, p. 182; A. Baltuska et al. in “Nature” vol.421, 2003, p. 611; and A. Baltuska et al. in “IEEE J. QE” vol. 9, 2003,p. 972. Control over the CE-phase of few-cycle pulses allowed studyingprocesses on time-scales shorter than the optical cycle, opening thedoor to attosecond metrology (1 as =10 ⁻¹⁸ s) and creating a newresearch field in physics dubbed ‘attoscience’, see R. Kienberger et al.in “Nature” vol. 427, 2004, p. 817; and E. Goulielmakis et al. in“Science” vol. 305, 2004, p. 1267. These Experiments need control overthe CE phase over long periods of time.

Two basic approaches have been described for stabilising the CE-phase.A. Baltuska et al. (“Nature” vol. 421, 2003, p. 611) have proposed astabilisation setup, which is illustrated in FIG. 8. With this setup,the CE-phase of a chirped-pulse amplifier 20′ is stabilised using twocontrol loops. In a first loop 40′ including an f-to-2f interferometer41′ and locking electronics 42′, a seed oscillator 10′ is stabilised. Inthe second loop 50′ including another f-to-2f interferometer 51′, anoffset is applied to the oscillator locking electronics 42′ in order tostabilise the CE phase at the output of the amplifier 20′. The phasestabilisation of the oscillator 10′ is forced to change the carrierenvelope phase of the pulses seeded into the amplifier. This is achievedby changing the offset signal-value in the locking electronics 42′,which in fact causes a controlled phase slipping of the oscillatorpulses. The phase drift of the oscillator 10′ is stabilised to beexactly π/2 between two pulses, ensuring that every fourth pulse comingfrom the oscillator to have the same phase. This is done by locking thebeat signal to a quarter of the oscillator repetition rate. A frequencycan be locked to another frequency with a fast ‘up-down’ counter, byletting the counter increment with every period of the referencefrequency, and decrement with every period of the frequency to bestabilised. When the output value of the counter is filtered with alow-pass filter, an error signal is generated by comparing this valuewith a reference value. By changing the reference value, a controlledphase shift, proportional to the change of the reference value isintroduced.

The stabilisation setup of A. Baltuska et al. has a first disadvantageas it exploits an additional degree of freedom of the oscillator phaselocking electronics, potentially decreasing the quality of the lock.This decrease in quality of the lock can in fact be observed, andeventually causes the lock to break earlier than in the undisturbedcase. A further disadvantage is related to the fact that the lockingelectronics 42′ is adapted to be operated with the signal from a singleamplifier only. Efficient stabilising amplifier chains is excluded withthe technique of A. Baltuska et al.

C. Li et al. have proposed another stabilisation setup (“Optics letters”vol. 31, 2006, p. 3113), which is illustrated in FIG. 9. Again, twocontrol loops are used for stabilising the CE-phase of a chirped-pulseamplifier 20′, namely a first loop 40′ with the f-to-2f interferometer41′ and locking electronics 42′ for stabilising the seed oscillator 10′and a second loop 50′ with another f-to-2f interferometer 51′. Contraryto the technique of A. Baltuska et al., the second loop 50′ directlycontrols the amplifier 20′. The CE phase is stabilised by changing adistance of telescope gratings in a pulse stretcher 22′ of the amplifier20′. As a first disadvantage, the technique of C. Li et al. isrestricted to particular laser systems having a single amplifier only,which is operated with a grating based pulse stretcher. Grating basedpulse stretcher represent complex optical systems, wherein eachdisplacement of a grating causes additional undesired effects.Furthermore, the technique of C. Li et al. has an essential disadvantagein terms of the high sensitivity of stabilisation. Grating translationof about 1 μm yields a CE phase shift of more than 180°. Therefore, thepractical control range of grating translation is restricted to about 2μm or even smaller values, so that high precision drives are necessaryfor reliably stabilising the CE-phase.

An additional method has been demonstrated (M. Schätzel et al. in “Appl.Phys. B”, vol. 79, 2004, p. 1021) allowing to control the phase offew-cycle pulses. However, this method can not be applied to longerpulses, like those coming directly from amplifier systems, and it needsphase-stable input pulses to begin with.

It could therefore be helpful to provide an improved method ofstabilising a carrier envelop phase of laser pulses, which method iscapable to avoid the disadvantages of the conventional stabilisingtechniques. Furthermore, it could be helpful to provide an improvedstabilising device for stabilising the carrier envelop phase of laserpulses avoiding the disadvantages of the conventional optical setups.

SUMMARY

According to a first general aspect a CE-phase stabilising method isdisclosed, wherein laser pulses generated with a seed laser unit andamplified with at least one amplifier unit are stabilised by anadjustment of the optical path of the laser pulses in the at least oneamplifier unit, which adjustment includes an introduction of adispersive material into the optical path. The amount of dispersivematerial, i.e. the length of the optical path through the dispersivematerial is adjusted by positioning the dispersive material in theoptical path in dependence on an amplifier output signal. The inventorhas found that the sensitive grating adjustment proposed by C. Li et al.can be replaced by the introduction of the dispersive material, whichyields substantive advantages in terms of improved stability androbustness of CE-phase control. Another advantage is given by the factthat available laser devices can be simply upgraded with the amplifierloop and the dispersive material. By slightly changing the dispersion,in particular in the pulse stretcher or compressor, the CE-phase of theultrashort amplified pulses can be controlled, without significantlychanging the output pulse duration.

The term “dispersive material” used in the present specification refersto any transparent material being free of absorptions in the wavelengthrange of interest, in particular in the wavelength range from infraredvia visible to ultraviolet light. Generally, the dispersive material canhave a shape, which is selected in dependence on the particularrequirements of application.

According to a second general aspect a stabilising device is disclosedbeing arranged for stabilising the CE-phase of laser pulses, wherein thestabilising device in particular includes a dispersion setting devicebeing arranged for introducing a dispersive material into the opticalpath of an amplifier unit for amplifying laser pulses.

According to a third general aspect, a laser device is disclosed, whichcomprises a seed laser unit, like in particular a laser oscillator,being arranged for generating laser pulses, and the stabilising deviceaccording to the above second aspect. The laser device has theparticular advantage of generating laser pulses with stabilisedCE-phase, which allows new applications of the laser device, inparticular in the field of femtosecond physics or in the field ofoptical data transmission and processing.

Advantageously, there are no particular restrictions with regard to theposition of the dispersive material introduced into the optical path ofthe amplifier unit. According to a first example, the dispersivematerial is introduced into the optical path of the pulse stretcher ofthe amplifier unit. In this case, advantages result from the fact thatthe laser pulse have a relatively low intensity as they have not yetpassed a pulse amplifier of the amplifier unit. Accordingly, anyundesired effects, e. g. by non-linear interactions of the pulses withthe dispersive material are avoided. The laser beam is unexpanded andthe dispersive material can be provided with small size.

According to a further example, the dispersive material is introducedinto the optical path of a pulse compressor of the amplifier unit. Inthis case, advantages are obtained as the pulse compressor usuallyoffers free space for arranging and adjusting the dispersive material.For avoiding non-linear interactions of the pulses with the dispersivematerial, the laser beam can be expanded at least before a position ofintroducing the dispersive material.

As a further example, the dispersive material can be introduced directlyinto the optical path of the pulse amplifier included in the amplifierunit.

Advantageously, an exemplary method allows stabilising different stagesof chirped-pulse amplifier chains independently. The method can beupscaled to multi-stage chirped-pulse amplifier chains, in which thesame principle can be applied independently to every individual stage.Accordingly, with a further example, the laser pulses are amplified withat least one further amplifier unit, wherein the CE phase of laserpulses output by the further amplifier unit is stabilised with acorresponding further amplifier loop controlling an introduction ofdispersive material into the optical path of the at least one furtheramplifier unit.

The amplifier chain including a plurality of amplifier units, wherein anamplifier loop is provided with at least one of the amplifier units forcontrolling the CE-phase of the output pulses, represents an independentsubject.

According to an exemplary embodiment, the dispersive material comprisesat least one dispersive prism, which advantageously allows a precise andreliable introduction of dispersion into the optical path of theamplifier unit by a simple linear translation of the dispersive prism.

Accordingly, the dispersive material may be introduced into the opticalpath of the amplifier unit by a movement (in particular translation) ofthe dispersive material. In the case of a dispersive prism, adisplacement range is preferably selected to be larger than 5 μm andsmaller than 500 μm. Particularly preferred is a displacement range of10 μm to 100 μm. The inventor has found that smaller displacements maycause difficulties for a precise and reproducible setting of thedispersive material in the optical path. Larger displacements may havedisadvantages in terms of response time and available space.

The dispersive material may be introduced into the optical path of theamplifier unit with a piezoelectric translator. Piezoelectrictranslators have particular advantages as precise drives in particularin the above preferred displacement range.

According to a further exemplary embodiment, the step of generating theamplifier output signal comprises splitting a portion of pulsesamplified with the amplifier unit into an f-to-2f-interferometer,generating a fringe pattern with the f-to-2f-interferometer, andsubjecting the fringe pattern to a Fourier transformation.

According to an exemplary embodiment, the CE-phase is additionallycontrolled with a seed laser loop, which is arranged for stabilising theseed laser unit generating the laser pulses. With the seed laser loop,the CE-phase stabilisation by introducing dispersive material into theamplifier unit is made more effective.

BRIEF DESCRIPTION OF THE DRAWINGS

Further details and advantage will be described in the following withreference to the attached drawings, which show in:

FIG. 1: a schematic illustration of a laser device equipped with astabilising device;

FIG. 2: a graphical representation of a laser pulse to be subjected to astabilisation method;

FIG. 3: a schematic illustration of an exemplary embodiment of the laserdevice;

FIGS. 4 and 5: graphical representations of experimental resultsillustrating advantages obtained with the stabilisation method;

FIG. 6: a schematic illustration of another exemplary embodiment of thelaser device;

FIG. 7: a schematic illustration of a stabilised amplifier chain; and

FIGS. 8 and 9: conventional optical setups adapted for stabilising theCE-phase (prior art).

DETAILED DESCRIPTION

Exemplary embodiments are described in the following with exemplaryreference to a laser device 100 comprising a seed laser unit 10, anamplifier unit 20 and (optionally) a pulse shaping unit 30 (FIG. 1). Theseed laser unit 10 is stabilised with a seed laser loop 40, while theamplifier unit 20 is stabilised with an independent amplifier loop 50including an interferometer 51 and locking electronics 52. The amplifierunit 20 generally includes a pulse stretcher 22, a pulse amplifier 21and a pulse compressor 23.

The components 10 to 50 and the feature comprising the controlledintroduction of a dispersive material 53 into the optical path of theamplifier unit 20 are schematically illustrated in FIG. 1. It isemphasised that details of the laser device 100 can be implemented inpractice with the optical setups illustrated in FIG. 3 or 6 or withother alternative optical setups providing the corresponding functionsand effects of the laser device 100. Details of the optical components,the operation of the laser device and details of control loops are notdescribed in the following as far as they are known from prior art.

First, the carrier envelope phase stabilisation of the seed oscillator10 using the seed laser loop 40 is considered. In particular, the seedlaser loop 40 includes a f-to-2f-interferometer 41 with a photoniccrystal fibre and a Mach Zehnder set-up and locking electronic 42 whichare structured and operated as described e. g. by A. Baltuska in“Nature”, vol. 421, 2003, p. 611 or by T. Udem et al. in “Opt. Lett.”vol. 24, 1999, p. 881. As an alternative, the seed laser loop can beimplemented without the f-to-2f-interferometer, but rather with acombination of a non-linear crystal and a IR photodiode described withreference to FIG. 3 below.

The seed laser loop 40 is operated on the basis of the followingconsiderations. In any resonator, only those modes can exist, whichfulfill the simple condition that an integer number of oscillations fitin one roundtrip. So for a laser, only those wavelengths λ for which

λ=1 with 1 the cavity length, can exist in the resonator and thereforebe emitted through the output coupler. In the frequency domain, allmodes (with optical frequency ν) resonant in the laser are integermultiples of f_(rep)=1/T when T is the cavity roundtrip time, and hencef_(rep) the repetition rate. In case of a ideally mode-locked laser,this would ensure that all pulses emitted from the laser would have thesame carrier envelope phase, but this is not the case in real systems.The intracavity dispersion shifts the resonant modes such that they areno longer an integer multiple of the oscillator repetition rate f_(rep),but they are offset by a certain amount f_(offset), as is graphicallyshown in FIG. 2. FIG. 2 (thick lines) shows a frequency comb spectrum ofa femtosecond oscillator. The inset shows the pulse train correspondingto the frequency comb, which shows a clear π/2 phase shift between eachpulse. The thin lines show an extrapolation of the frequency comb, tomake the comb offset from zero visible. This offset is directly linkedto the phase-shift Δφ between two subsequent pulses emitted from theoscillator, such that: Δφ=2πf_(offset)/f_(rep). By stabilising theoffset frequency, the pulse to pulse phase-shift of the seed oscillatorcan be stabilised with the first loop 40, and pulses with the sameCE-phase can be selected for amplification as described e. g. by A.Baltuska in “Nature”, vol. 421, 2003, p. 611.

Generally, the oscillator pulse-to-pulse phase shift is stabilised to beπ/2, so pulses with the same CE phase are selected by dividing theoscillator repetition rate by an integer multiple of 4. Because therepetition rate of amplifier systems is so much lower than that of theseed oscillator, this imposes practically no limitations on theamplifier repetition rate. Although the carrier envelope phase of thepulses picked for amplification is the same, it is not the case afteramplification. Measurements of the carrier envelope phase drift afteramplification have shown, that the carrier envelope phase drifts over afew radians in several seconds, thus over several thousands of laserpulses.

This slow drift originates from different sources, the most prominent ofwhich are energy fluctuations of the pump laser and the seed oscillator,and beam pointing fluctuations. As the drift of the CE-phase isrelatively slow, it is possible to compensate for it by means of theamplifier loop 50. The phase drift is compensated with the method basedon a phase shift introduced by the dispersive material 53 (or:dispersion) into the beam path. For example by changing the amount ofglass in the beam path by a few micrometers, the carrier envelope phasecan be changed significantly.

According to FIG. 3, this approach is implemented by transversallyshifting one of the prisms in the pulse compressor 23. The seed laserunit 10 comprises a Ti:sapphire oscillator 11, the output laser pulsesof which are focussed into a non-linear crystal 12 and transmittedthrough a dichroic mirror 13 to the input of the pulse stretcher 22 ofamplifier unit 20. The non-linear crystal 12 comprises a periodicallypoled MgO:LN crystal being arranged for difference frequency mixing. Aportion of the laser pulses is split to an IR photodiode 14. TheTi:sapphire oscillator 11 is e. g. a “Femtosource Rainbow” (Femtolasers,Vienna, Austria).

The non-linear crystal 12 and the IR photodiode 14 are arranged forimplementing the seed laser loop stabilising the seed laser unit 10 (seeFIG. 1). With the non-linear crystal 12, frequency components of thelaser pulse spanning an octave (f, 2f) are superposed. The output of thenon-linear crystal 12 is measured with the IR photodiode 14 yielding acontrol signal for locking electronics (not shown in FIG. 3) stabilizingthe oscillator 11 of unit 10.

The amplifier unit 20 comprises the pulse stretcher 22, the pulseamplifier 21 and the pulse compressor 23. The pulse stretcher 22 isarranged for stretching the laser pulses from about 5 fs to about 15 ps.To this end, the pulse stretcher 22 includes a material with positivedispersion, like e.g. a glass block made of the highly dispersive SF 57glass and so-called TOD mirrors (with third- and fourth-orderdispersion). As an example, the pulse stretcher is structured asdescribed by S. Sartania et al. in “Optics Letters”, vol. 2, 1997, p.1563. The pulse amplifier 21 comprises a multipath resonator, e.g. a9-pass chirped pulse amplifier with a repetition rate of 3 kHz.

After amplification, the laser pulses are subjected to pulse compressionin the pulse compressor 23. The pulse compressor 23 is a prismcompressor including compressor prisms 24, which are arranged foradjusting the pulse duration. The dispersive prism 53, which is one ofthe compressor prisms, is adapted for further adjusting the optical pathin the pulse compressor 23 to control the CE-phase of the laser pulses.To this end, the dispersive prism 53 is arranged on a piezo-actuatedtranslation stage 54. The translation stage 54 is arranged fordisplacing the prism with a distance on a micrometer scale. Theinsertion of the compressor prisms 24 in the prism pulse compressor 23controls the pulse duration by varying the amount of material on theorder of millimetres. Furthermore, the CE-phase is varied by displacingthe dispersive prism 53 on the order of micrometers.

In the case of fused silica as a dispersive material 53 and pulses witha central wavelength of 800 nm, as is the case for the Ti:sapphire lasersystem used, addition of approximately 50 μm of material, introduces aCE-phase shift of 2π, without noticeably lengthening the pulse.Advantageously, no additional optical components need to be introduced,and strictly taken, not even a degree of freedom is added to theamplifier, since the material dispersion in the prism compressor 23 isalso used for optimising the pulse duration. The translation stage 54can be provided with another one of the compressor prisms. Transversallyshifting one of the compressor prisms over a few micrometers will notaffect the pulse duration, but it strongly modifies the CE-phase. Inother words, the function of dispersion control can be fulfilled by oneof the compressor prisms without an essential variation in pulseduration.

Alternatively, the dispersive material can be introduced as anadditional component into the optical path in the compressor 23. As anexample, a pair of two prisms can be provided in an analogue way asshown in FIG. 6.

The CE-phase is stabilised with the amplifier loop 50. At the output 25of the pulse compressor, a small portion (about 0.7%) of the compressedlaser pulses is split into the amplifier loop 50, while the main portionof the compressed laser pulses is guided to the pulse shaping unit 30.The amplifier loop 50 comprises the f-to-2f interferometer 51 beingarranged for generating an optical amplifier output signal and thelocking electronic 52 for controlling the dispersion prism 53 in thepulse compressor 23. Locking electronic 52 includes a spectrum analyser,a processing unit and a DA output card. The processing unit includes acomputer, which is arranged for reading the spectrum measured with thef-to-2f interferometer 51 and calculating a feedback signal from this.For operating the amplifier loop 50, the fringe-pattern measured at theoutput of the f-to-2f interferometer 51 is Fourier-transformed. Thephase at the delay-point of the fringes corresponds to the CE-phase. Themeasured phase of the fringe-pattern represents an amplifier outputsignal, on the basis of which a proportional feedback signal is providedfor setting the translation stage 54 with the dispersive material 53.The corresponding calculations are implemented as demonstrated by A.Baltuska et al. in “IEEE J. QE” vol. 9, 2003, p. 972. The feedbacksignal is applied with the translation stage under one of the prisms inthe prism compressor, preferably to dispersive prism 53. Alternatively,the feedback signal can be applied to one of the remaining prisms, e. g.one or more of the compressor prisms 24.

The pulse shaping unit 30 receives the compressed pulses from the pulsecompressor 23. The compressed pulses have e.g. an energy of 1 mJ and aduration of 25 fs. The laser pulses are guided through a neon filledhollow fibre 31 and a further chirped mirror pulse compressor 32, theoutput of which comprises laser pulses with e.g. 400 μJ energy and 5 fspulse duration. Subsequently, the laser pulses are guided to amonitoring device 60 including e.g. an autocorrelator 61, which used formonitoring pulse duration after the hollow fibre 31. Optionally, anabove-threshold ionisation detector device 62 can be provided, which isused for experimentally monitoring the phase stability of the pulses asdescribed below. After passage through the monitoring unit 60, the laserpulses are output to the further application, like e.g. an experiment oran optical signal processor.

In FIGS. 4A and 4B, the compensation of the CE-phase drift with theconventional method (FIG. 8) and the method is shown, respectively. Thetwo traces 4A and 4B were recorded both within a short period of time,ensuring that all other experimental conditions have not changedsignificantly. One can clearly see that the method results in a smallerRMS phase noise. The method features a smaller RMS phase noise, 0.15 radversus 0.19 rad for the conventional method. The reason that the phasenoise in the conventional case is larger originates from the fact thatthe feedback could not be made stronger without degrading the oscillatorstability significantly.

As a further advantage, the inventor has found that the stabilisationcan be reliably operated on a time scale of 30 hours or even more up toone week. This represents an essential development compared withconventional techniques which allowed a stabilisation within some hoursonly. In particular, experiments yielding only a few measurable eventse. g. per minute can be conducted for measuring sufficient signalsallowing an appropriate statistical analysis.

The result of an experiment proving that the method is functioningcorrectly is presented in FIG. 5. With the above-threshold ionisationdetector device 62, an ionization measurement can be performed asdescribed by G. G. Paulus et al. in “Phys. Rev. Lett.” vol. 91, 2003, p.253004 and M. Schätzel et al. in “Appl. Phys. B”, vol. 79, 2004, p.1021, to confirm the phase stability with the method. When the CE-phaseof the amplifier is stabilised with a slow feedback from the f-to-2finterferometer 51 with the method, the phase measurement with theabove-threshold ionisation detector device 62 can be used as anout-of-loop measurement to determine the quality of the phase-lock ofthe amplifier. In FIG. 5, the result of this measurement can be seen.The RMS phase noise measured in-loop with the f-to-2f interferometer 51was 0.15 rad (lower curve), while the RMS phase noise measuredout-of-loop with the above-threshold ionisation detector device 62 was0.23 rad (upper curve), confirming that the method stabilises theCE-phase correctly.

FIG. 6 shows another exemplary embodiment with a schematicallyillustrated laser device 100 comprising the seed laser unit 10 and theamplifier unit 20 including the pulse stretcher 22, the pulse amplifier21 and the pulse compressor 23. The amplifier unit 20 is stabilised withthe amplifier loop 50 including the interferometer 51 and lockingelectronics 52. According to FIG. 6, the stabilisation approach isimplemented by introducing a pair of Brewster-prisms 53 as dispersivematerial into the pulse stretcher 22 before amplification.

A small split-off from the output pulses of the pulse compressor 23 isfed into the f-to-2f interferometer 51. The CE-phase is stabilised withthe locking electronics 52 as described above. The feedback is appliedwith a piezo-actuated translation stage 54 on which one of the Brewsterprisms 53 in the pulse stretcher 23 is mounted. Translation of a fewmicrometers of the prism is enough to change the CE-phase significantly.

Another advantage of the method is, because it operates independent ofany other feedback, that it can be applied multiple times in one system.For amplifier chains, this approach is therefore the only possible. InFIG. 7 this is drawn schematically for a multiple stage chirped-pulseamplifier system 101 comprising a seed laser unit 10 with a seed laserloop 40 and amplifier units 20.1, 20.2 each including a pulse stretcher,a pulse amplifier and a pulse compressor 23. Each amplifier unit 20.1,20.2 is stabilised with an associated amplifier loop 50.1, 50.2,including an interferometer 51.1, 51.2 and locking electronics 52.1,52.2. Each stabilisation is implemented according to the controltechnique described above.

The amplifier system 101 can include more than the two amplifier units20.1, 20.2, e. g. up to 5 amplifier units. This approach allows to scalethe control of the CE-phase to ultrashort pulses in the petawatt (1015W) regime.

The features disclosed in the above description, the drawings and theclaims can be of significance both individually as well as incombination for the realization of the aspects disclosed and its variousforms.

1.-17. (canceled)
 18. A method of stabilizing a carrier envelope phaseof laser pulses generated with a laser device, comprising the steps of:generating laser pulses with a seed laser unit, amplifying the laserpulses with an amplifier unit, generating an amplifier output signalderived from the laser pulses amplified with the amplifier unit, andcontrolling the carrier envelope phase of the laser pulses with anamplifier loop based on the amplifier output signal, wherein thecontrolling step comprises a step of adjusting an optical path of theamplifier unit in dependence on the amplifier output signal, wherein theadjusting step comprises: introducing a dispersive material into theoptical path of the amplifier unit.
 19. A method according to claim 18,wherein the adjusting step comprises: introducing the dispersivematerial into the optical path of a pulse compressor or a pulsestretcher included in the amplifier unit.
 20. A method according toclaim 18, wherein the step of generating the amplifier output signalcomprises: coupling a portion of the amplified pulses into anf-to-2f-interferometer, generating a fringe pattern with thef-to-2f-interferometer, and subjecting the fringe pattern to a Fouriertransformation.
 21. A method according to claim 18, comprising thefurther steps of: amplifying the laser pulses with at least one furtheramplifier unit, generating at least one further amplifier output signalderived from the laser pulses amplified with the at least one furtheramplifier unit, and controlling the carrier envelope phase of the laserpulses with at least one further amplifier loop, wherein the controllingstep comprises introducing a further dispersive material into an opticalpath of the at least one further amplifier unit in dependence on the atleast one further amplifier output signal.
 22. A method according toclaim 21, wherein the laser device comprises a chain of amplifier unitsand the carrier envelope phase of the laser pulses output by the chainof amplifier units is controlled by introducing dispersive material intothe optical path of each of the amplifier units.
 23. A method accordingto claim 18, wherein the step of introducing the dispersive materialcomprises: setting a dispersive prism in the optical path of therespective amplifier unit.
 24. A method according to claim 23, wherein aposition of the dispersive prism is set by a translation of thedispersive prism in the range of 5 μm to 500 μm.
 25. A method accordingto claim 18, comprising the steps of: generating a seed laser outputsignal derived from the laser pulses generated with the seed laser unit,and controlling the carrier envelope phase of the laser pulses with anseed laser loop based on the seed laser output signal.
 26. A stabilizingdevice for stabilizing a carrier envelope phase of laser pulses,comprising: an amplifier unit arranged for amplifying laser pulses, anamplifier output signal generator arranged for generating an amplifieroutput signal derived from the laser pulses, an amplifier loop arrangedfor controlling the carrier envelope phase of the laser pulses based onthe amplifier output signal, and a dispersion setting device arrangedfor introducing a dispersive material into an optical path of theamplifier unit in dependence on the amplifier output signal.
 27. Astabilizing device according to claim 26, wherein the dispersion settingdevice is arranged in the optical path of the pulse compressor or thepulse stretcher.
 28. A stabilizing device according to claim 26, whereinthe amplifier loop comprises a f-to-2f-interferometer and a Fouriertransformation unit coupled with the dispersion setting device.
 29. Astabilizing device according to claim 26, further comprising: at leastone further amplifier unit arranged for amplifying laser pulses, atleast one further amplifier output signal generator arranged forgenerating at least one further amplifier output signal derived from thelaser pulses, at least one further amplifier loop arranged forcontrolling the carrier envelope phase of the laser pulses based on theat least one further amplifier output signal, and at least one furtherdispersion setting device arranged for introducing a dispersive materialinto an optical path of the at least one further amplifier unit independence on the at least one further amplifier output signal.
 30. Astabilizing device according to claim 26, wherein the dispersivematerial comprises a dispersive prism and the dispersion setting deviceis arranged for setting the dispersive prism in an optical path of theamplifier unit in dependence on the amplifier output signal.
 31. Astabilizing device according to claim 30, wherein the dispersion settingdevice is arranged for setting the position of the dispersive prism inthe range of 5 μm to 500 μm.
 32. A stabilizing device according to claim26, wherein the dispersion setting device comprises a piezoelectrictranslator.
 33. A laser device, comprising: a seed laser unit arrangedfor generating laser pulses, and at least one stabilizing deviceaccording to claim 26, being arranged for stabilizing a carrier envelopephase of the laser pulses generated with the seed laser unit.
 34. Alaser device according to claim 33, further comprising: a seed laseroutput signal generator arranged for generating a seed laser outputsignal derived from the laser pulses, and a seed laser loop arranged forcontrolling the carrier envelope phase of the laser pulses based on theseed laser output signal.